A method for suppressing infrared radiation from an engine of an aircraft operating in an environment includes directing hot exhaust from the aircraft engine into a lobed mixer of a single baffle infrared suppressor having a collapsible, translatable baffle to generate alternating flows of hot exhaust gas and cold air. The method further includes directing the alternating flows of hot exhaust gas and cold air towards the single baffle assembly to mix the hot exhaust gas with the cold air.
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1. A method for suppressing infrared radiation from an engine of an aircraft operating in an environment, said method comprising:
directing hot exhaust from the aircraft engine into a lobed mixer of a single baffle infrared suppressor having a collapsible, translatable baffle to generate alternating flows of hot exhaust gas and cold air; and
directing the alternating flows of hot exhaust gas and cold air towards the collapsible, translatable baffle to mix the hot exhaust gas with the cold air.
10. An infrared suppressor for suppressing infrared radiation from an engine of an aircraft operating in an environment, said infrared suppressor comprising:
a stage I duct configured to direct hot exhaust from the aircraft engine towards a stage ii duct;
a gap around the stage I duct configured to channel a flow of cold air towards said stage ii duct; and
a lobed mixer of a single baffle assembly having a collapsible, translatable baffle positioned in said stage ii duct, said single baffle assembly configured to generate alternating flows of hot exhaust gas and cold air.
19. An infrared suppressor for suppressing infrared radiation from an engine of an aircraft, said infrared suppressor comprising:
a stage I duct having an adapter ring configured to slide over a tailpipe of the engine and a lobed mixer;
a stage ii duct coupled to said stage I duct and having a collapsible and translatable single baffle assembly, said stage ii duct configured to receive exhaust from the engine that leaves said stage I duct; and
a stage iii duct coupled to said stage ii duct and configured to receive exhaust from the engine that leaves said stage ii duct, said stage iii duct comprising a hood and a panel that are at least one of positionable or rotatable to turn exhaust leaving said stage iii duct.
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This invention relates generally to infrared suppression devices and more generally to methods and apparatus for reducing infrared emission from gas turbines such as those used, for example, in helicopters.
In some helicopters used in hostile environments, gear boxes under helicopter rotors are driven by gas turbine engines. These engines rotate at very high RPM, although the helicopter rotors themselves rotate at low RPM because of their diameter. The tailpipes of the gas turbine engines are exhausted overboard. The tailpipe becomes very hot from this hot exhaust gas and thus provides a very bright infrared signal.
With recent advancements in weapons detection technology, there is growing recognition of the importance of reducing the infrared signature associated with gas turbine engines powering military aircraft and land combat vehicles. Signature reductions reduce the possibility of detection and pursuit by enemy anti-aircraft forces including heat-seeking missiles. At least two known configurations have been used to suppress infrared radiation from gas turbine engines. One of these configurations has a center plug is disposed in an exhaust flow that cooperates to block a line of sight to hot turbine parts of the engine. Another blocks the line of sight by ejecting hot gases from the suppressor at a substantial angle from the axial center line of the engine.
An example of an infrared suppressor is disclosed in U.S. Pat. No. 4,295,332, Steyer et al, which describes the use of splitters that perform a dual function of mixing hot and cool gas flows to reduce gas temperatures and also block line-of-sight infrared radiation. Since the conception of the suppressor disclosed in U.S. Pat. No. 4,295,332, additional developments have made possible even more compact and higher performance suppressor construction arrangements. However, even as suppressor construction arrangements have improved, threats have also improved and engine exhaust gas temperatures have been increasing as requirements for increased power and reduced weight have been imposed.
Moreover, current infrared suppression solutions trade performance, payload capability, and/or range for improved survivability. Applicants believe that all currently fielded rotorcraft infrared suppression systems are static systems. For example, one system described in U.S. Pat. No. 6,253,540 provides infrared suppression using static line of sight blockage and the mixing of exhaust gasses with cooling air via ejector action.
Some aspects of the present invention therefore provide a method for suppressing infrared radiation from an engine of an aircraft operating in an environment. The method includes directing hot exhaust from the aircraft engine into a lobed mixer of a single baffle infrared suppressor having a collapsible, translatable baffle to generate alternating flows of hot exhaust gas and cold air. The method further includes directing the alternating flows of hot exhaust gas and cold air towards the single baffle assembly to mix the hot exhaust gas with the cold air.
Other aspects of the present invention provide a method for suppressing infrared radiation from an engine of an aircraft operating in an environment. The method includes directing hot exhaust from the aircraft engine into a lobed mixer of a single baffle infrared suppressor to generate alternating flows of hot exhaust gas and cold air. The method further includes directing the alternating flows of hot exhaust gas and cold air towards the single baffle assembly to mix the hot exhaust gas with the cold air, and positioning a hood and a panel of the infrared suppressor in accordance with the threat environment.
Still other aspects of the present invention provide a method for suppressing infrared radiation from an engine of an aircraft operating in an environment. The method includes directing hot exhaust from the aircraft engine into a lobed mixer of a single baffle infrared suppressor to generate alternating flows of hot exhaust gas and cold air. The method further includes directing the alternating flows of hot exhaust gas and cold air towards the single baffle assembly to mix the hot exhaust gas with the cold air, and selecting a mode of operation from a set of modes. The set of modes includes a first mode in which a direct view of an exhaust cavity is blocked, a second mode that pumps and blocks a line-of-sight into the engine, and a third mode in which backpressure is minimized or reduced.
Yet other aspects of the present invention provide an infrared suppressor for suppressing infrared radiation from an engine of an aircraft operating in an environment. The infrared suppressor is configured to direct hot exhaust from the aircraft engine into a lobed mixer of a single baffle assembly having a collapsible, translatable baffle to generate alternating flows of hot exhaust gas and cold air. The suppressor is further configured to direct the alternating flows of hot exhaust gas and cold air towards the single baffle assembly to mix the hot exhaust gas with the cold air.
Yet additional aspects of the present invention provide an infrared suppressor for suppressing infrared radiation from an engine of an aircraft operating in an environment. The suppressor is configured to direct hot exhaust from the aircraft engine into a lobed mixer of a single baffle assembly having a collapsible, translatable baffle to generate alternating flows of hot exhaust gas and cold air. The suppressor is further configured to direct the alternating flows of hot exhaust gas and cold air towards the single baffle assembly to mix the hot exhaust gas with the cold air. The infrared suppressor also comprises a hood and a panel that are repositionable in accordance with the threat environment.
Still other aspects of the present invention provide an infrared suppressor for suppressing infrared radiation from an engine of an aircraft operating in an environment. The infrared suppressor is configured to direct hot exhaust from the aircraft engine into a lobed mixer of a single baffle assembly having a collapsible, translatable baffle to generate alternating flows of hot exhaust gas and cold air. The suppressor is further configured to direct the alternating flows of hot exhaust gas and cold air towards the single baffle assembly to mix the hot exhaust gas with the cold air, and operate in a set of modes. The set of modes includes a first mode in which direct view of an exhaust cavity is blocked and which facilitates high infrared suppression when the aircraft is under threat, a second mode which blocks a line-of-sight into the engine and which represents a compromise between suppression and performance for some protection in hostile environments, and a third mode in which backpressure is minimized or reduced which facilitates high performance for emergency situations or benign environments.
Yet further aspects of the present invention provide an infrared suppressor for suppressing infrared radiation from an engine of an aircraft. The infrared suppressor includes a stage I duct, a stage II duct, and a stage III duct. The stage I duct has an adapter ring configured to slide over a tailpipe of the engine and a lobed mixer. The stage II duct is coupled to the stage I duct and has a collapsible and translatable single baffle assembly. The stage II duct is configured to receive exhaust from the engine that leaves the stage I duct. The stage III duct is coupled to the stage II duct and configured to receive exhaust from the engine that leaves said stage II duct. The stage III duct includes a hood and a panel that are positionable and/or rotatable to turn exhaust leaving the stage III duct.
Configurations of the present invention will thus be seen to provide considerable IR suppression of engines when required for survivability while providing the capability to minimize loss of performance, thus increasing payload capability, and/or range in more benign environments. In particular, some configurations provide a first mode the provides for high IR suppression in hostile environments, a second mode that provides some blockage of engine hot parts, and a third mode that provides high performance for benign environments.
In some configurations and referring to
Lobes 22 are spaced from one another in two rows. Lobes 22 are spaced in two horizontal rows perpendicular to the plane of
Flow A, coming from the left in
As the hot, high pressure exhaust flow races through stage II duct 16 it draws ambient, cool, outside air through opening 24. The flow of hot air between lobes 22 and over forward baffle 26 surface 28 draws cold air through opening 24 as a result of a reduction in pressure. The cold air drawn through opening 24 passes alongside columns of hot air, thereby cooling an exiting gas stream flowing up and over baffle 42, from which the exiting gas stream flows into stage III duct 20, which acts as another ejector nozzle that pulls in more cold air into voids denoted by 34 and 90 and into opening 33, all of which are open to the atmosphere.
Forward baffle 26 splits the hot, high pressure exhaust flow into two paths B and C. Forward baffle 26, which is substantially “V” shaped may include, in some configurations, a strut or other supporting structure 32. Forward or hot baffle 26 and cold baffle 42 together comprise a single baffle assembly, distinguishing it from previous designs that utilize a plurality of baffle assemblies. Cold baffle 42 is used to shield forward or hot baffle 26 as seen from an exit direction (i.e., looking into the exhaust exit of stage III duct 20). As used herein, a “single baffle assembly” is defined as a combination of a single hot baffle and a single cold baffle. Lobes 22 may also be present in a single baffle assembly, as may shields 38, further described below. However, an assembly having a plurality of forward or hot baffles, a plurality of cold baffles, or a plurality of both, is excluded from the term “single baffle assembly,” and rather is referred to herein as a “plural baffle assembly.” Moreover, a “single baffle infrared suppressor,” such as infrared suppressor assembly 10, is referred to herein as a “single baffle infrared suppressor” configuration when it includes exactly one single baffle assembly and no plural baffle assemblies.
A cold air flow is guided into a recess or void 90 inside cold baffle 42, drawn from inlets 33. This air is drawn around into the top and bottom surfaces of cold baffle 42 (as shown in
Thus, a combination of holes or slits that allow air to enter void 34, the ejector action of forward baffle 26 drawing cold air upward and downward, and the guiding action of shields 38, a sheet of cold air mixes with hot exhaust exiting around forward baffle 26.
Line of sight shields (not shown in the Figures) can be provided to prevent a viewer looking upstream from exhaust end 35 from seeing hot parts of stage I duct 14. For example, mixer lobes 22 would normally be running hot because there is hot gas flowing underneath it. Line of sight shields can be added to prevent an observer from viewing lobes 22 looking into exhaust end 35.
Referring to
Some ambient cold air not entering lobes 22 flows through gap 24 into a region between surfaces 28 of forward baffle 26 and wall 54. This flow is made clearer by reference to
Stage I duct 14 can be referred to as a “lobed mixer,” because of the presence of lobes 22 and the mixing of cold ambient air in lobes 22 with the hot exhaust between lobes 22.
More particularly, hot exhaust gasses from an aircraft engine are directed into the lobed mixer of single baffle infrared suppressor 10, which includes a single baffle assembly comprising forward or hot baffle 26, cold baffle 42, and shields 38. The direction of hot exhaust from the engine in conjunction with cold air entering through gap 24 generates alternating flows of hot exhaust gas and cold air. These alternating flows are directed towards the single baffle assembly to mix the hot exhaust gas with the cold air to cool the emission from the engine to thereby reduce infrared emissions. The practical use of a single element baffle assembly in a single baffle infrared suppressor 10 is made possible by, among other things, the use of a lobed mixer. This mixer rapidly and effectively mixes engine bay cooling air in the engine exhaust with cold air to reduce or eliminate hot streaks, which are portions of unmixed engine exhaust air. These hot streaks are a strong plume signature contributor, a source of radiation heat transfer to stage II duct walls, and where it persists further into suppressor 10, a source of hot streaks in stage II or stage III walls. Hot streaks cause the exhaust plume to become a significant contributor to an IR signature at close range. In various configurations, an additional flow path of cold air guided in part by segments 62 between lobe inlets 30 is provided so that the hot exhaust flows are surrounded on three sides by cold air.
To summarize, a flow of hot exhaust air flows into stage I duct 14, and is split into two flows B and C after going through a mixer that comprises stage II duct 16. Cold air is injected or entrained into the hot air stream, slowing down and cooling the air, as well as increasing the mass flow (by about 50% in some configurations). Surfaces of forward baffle 26 become hot, so a second injector comprising a cold air inlet 33 injects additional cold air to cool inner surfaces of suppressor 10 and shield hot surfaces from visibility. Additionally, forward baffle 26 is shielded from view from the back end of suppressor 10 by cold baffle 42 and shields 38. Cold air entering from voids 34 is distributed laterally, and cools cold baffle 42. Thus, when infrared suppressor assembly 10 is viewed from any direction, there is very little or no hot air or hot surface area visible. In addition to being very effective at suppressing infrared emissions, assembly 10 is also relatively simple and low weight.
A purged air flow P comes from the left and right sides through a gap 24 as viewed from the vantage point of
A cooling dilution flow is increased by controlling the size of areas of flow through suppressor 10. For example, the exit of stage I duct 14 is smaller and has one or more relatively large gaps 24 for cold air to enter. Discrete rectangles of hot and cold gasses (i.e., the hot air flows F and the cold flows through gaps 62 and exiting at lobe exits 58) are sized so that the hot gas that comes through is in a relatively small interlobe gap. The rectangles having the hot gas are narrowly sized (as is shown in
The flow of gasses through suppressor 10 is also contoured. Whereas known prior art suppressors had a stage II duct 16 barely fitting into a stage III duct 20, some configurations of the present invention have a stage III duct 20 that parallels stage II a much longer distance. In this manner, stage III duct 20 thus has an extended inlet flowpath through gap 33. In the known prior art configurations, for example, the amount that stage II duct 16 fits into stage III duct 20 is just enough to allow the ducts to stay put when connected with spacers. A substantially greater overlap is provided to improve cooling of stage II walls 37.
In various configurations of the present invention, a coating, or combination of coatings, is used on surfaces to further suppress infrared radiation. Any suitable coating may be used, including black spray paint. However, increased durability and performance may be achieved with other coatings, including various proprietary and non-proprietary coatings known in the art for use with suppressors.
The total angle of the bend in curved stage I duct 14 in some configurations of the present invention is at least about a 15 degree change in the axis from adapter ring 12 and gap 24. This bend results in the axis of suppressor 10 being about 15 degrees tilted with respect to an attached engine. In some configurations, the angle of the bend and the tilt can be as high or higher than 30 degrees. From gap 24 aft, some configurations (not shown in the Figures) provide additional curvature. The bending of the axis of suppressor 10 is not required in all configurations of the present invention, and can be provided at various angles dependent upon the aircraft on which suppressor 10 is to be used. In general, the bend is limited in that suppressor 10 has to fit the aircraft engine and structure. In some configurations, the bend is away from the fusilage of the aircraft.
It will thus be evident that configurations of the present invention provide improved protection against threats even with increased engine exhaust gas temperatures and requirements for increased power and reduced overall weight. In particular, the lobed mixer rapidly and effectively mixes engine bay cooling air into the engine exhaust to reduce or eliminate hot streaks that otherwise would be a strong plume signature contributor, a source of radiation heat transfer to the stage II walls, and even a generator of hot streaks in the stage II and stage III walls. The lobed mixer thus has a significant benefit on IR signature reduction. The use of shields 38 also reduce the signature from slightly above and below the suppressor axis in a purged air space. In some configurations, overall cooling/dilution flow is significantly increased to 1.5:1, resulting in significantly reduced plume temperatures to reduce plume signature, suppressor core heat load, and aircraft fuselage heat load. In addition, an extended and contoured inlet flowpath provides a more uniform stage III cooling film and “backside” cools the stage II wall. In configurations in which the suppressor axis is realigned outboard, the suppressor exhaust is directed further outboard to prevent its washing the aft fuselage, resulting in a significant signature reduction from the aircraft.
In yet other configurations of the present invention, instead of a fixed baffle configuration represented by
More particularly,
Shields 38 are replaced by similar shields 138 that differ from shields 38 in that shields 138, or cold baffle 142, are attached to rods 308 that join at a pivot or hinge axle 320 (better seen in
The amount of height change and direction of translation are different for the first and third mode. Some configurations, provide variability in stage III duct 20 using a moveable deflectors comprising hood 408 and lower panel 422, and/or an upper panel, as shown in
In the second mode, collapsible baffle 126 is opened up at a downstream end of stage I duct 14 to increase pumping and blocking a line-of-sight into an attached engine (not shown in the Figures). This second mode provides protection in a hostile environment without incurring all of the penalties of the redirected flowpath of the first mode. In some configurations, an approximately 74% infrared signature reduction from conventional infrared suppression levels is achieved at tail-on, and an approximately 71% infrared signature reduction at side view.
In the third mode, an unsuppressed, low backpressure mode is achieved by actuating collapsible baffle 126 to its collapsed position (as shown in
In the third mode, infrared suppression apparatus 10 is providing substantially the same exhaust configuration as a conventional IR suppressor, but with the baffle removed, which can provide installed engine performance slightly better than the that of an unsuppressed engine.
More particularly, in the third mode, deflector hood 408 and panel 422 are essentially oriented axially with respect to suppressor 10 to direct flow aft. In the first mode, however, deflector hood 408 and panel 422 are repositioned and/or rotated to turn the exhaust flow.
In various configurations of the present invention, mode selection can be selected manually by a pilot, automatically by a combination of a Full Authority Digital Engine Control (FADEC) and threat warning sensors, and/or by a combination of the foregoing.
In some configurations, the second mode provides a single element baffle 126 that eliminates characteristically higher temperatures of suppressors having multiple baffles. The lobed stage I duct exit mixer eliminates plume hot streaks, and the lobes are hidden from line of sight by the single element baffle. An increased bypass ratio of from about 0.8 to 1 to about 1.5 to 1 is provided for reduced hot metal and external plume signature. In some configurations, titanium metal is used in the construction of suppressor 10 for weight reduction. Also, suppressor 10 is aligned 15 degrees further outboard to reduce fuselage heating. Moreover, in other embodiments, a coating or suite of coatings may be applied to enhance the device's emission suppression capabilities.
It will thus be appreciated that configurations of the present invention provide considerable IR suppression of engines when required for survivability, while providing the capability to minimize loss of performance, payload capability, and/or range in more benign environments. In particular, the first mode provides for high IR suppression in hostile environments, mode two provides some blockage of engine hot parts, whereas the third mode provides high performance for benign environments.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
Steyer, William, Tingle, Walter J., Kieffer, Christopher Marlow
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